Character image generating system, storage medium storing character image generating program and method

ABSTRACT

The present invention is a character image generation system for generating outline font based on character information and displaying the outline font on a display with a prescribed number of pixels. The character image generation system subdivides a curve expressed by character outline information corresponding to inputted character information, calculates the difference between coordinates at each end of the subdivided curve, compares the difference with a predetermined threshold value and sequentially calculates coordinates for each pixel, based on this comparison result.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the generation of character images.

2. Description of the Related Art

The spread of portable equipment, such as a cellular phone, a personaldigital assistant (PDA) and the like, is remarkable. Therefore,attention is paid to character images displayed on a portableequipment-mounted flat panel type display device used for portableequipment.

Conventionally, in portable equipment, dot font has been used ascharacter to be installed inside beforehand and be displayed since itsprocessing capacity is low. Conventionally, the processing capacity andgraphic performance of built-in equipment is low. Therefore, the use ofdot font by which a necessary character image can be stored in memorywithout being processed and be developed on a screen was efficient.

However, character images with a design could not be expressed in abinary image by dot font.

FIG. 1 shows jaggies caused by the change of resolution when using dotfont. As shown in FIG. 1, the lower resolution is (the larger the numberof dots is), the coarser displayed characters become.

The high liquid crystal device (LCD) panel resolution of a cellularphone in the market is approximately 140 ppi. When displaying charactersof approximately 3.5 mille-meters, which can be easily seen on an LCDscreen, the size of pixels constituting one character on theabove-mentioned panel is approximately 20 dots by 20 dots. The largenumber of strokes (number of sides) of a Japanese character isapproximately 10 to 12. Therefore, when displaying a complex characterwith a large number of strokes, the character had to be deformed. Forexample, a part of the character had to be omitted.

Recently, the resolution of an LCD panel used for built-in equipment hasexceeded 180 dpi and the number of clocks as the processing capacity ofa CPU has increased to 100 to 200 MHz, which is a PC level 10 years ago.Therefore, a graphic library could be made operable. In cellular phones,the demand of character images with a design has increased. Furthermore,with the promotion of a fine screen, the capacity of character imageshas increased, which has raised a problem of the shortage of memorycapacity. In such a situation, recently needs for installing outlinefont in built-in equipment have increased.

In order to faithfully reproduce a character design, a method fordigitalizing curves composing a character and reproducing its charactershape according to a supplied character size is generally used. Theoutline font is used one example of such a method (for example, seeJapanese Published Patent Application Nos. 05-019739 and H05-143742).

The outline of the outline font is digitalized as a straight line and anapproximate curve. Typical approximation curves include Bezier curve,spline curve and the like. In the case of the Bezier curve, as data, astarting point, an endpoint and several control points for interpolatingbetween them are used. A closed curve can be calculated by using thesepoints and a character image can be generated by painting over theinside of the closed curve.

FIG. 2 shows an example of a character expressed by the functionalexpression of Bezier curve. As shown in FIG. 2, a Chinese character iscomposed of a plurality of points and curves between them. As a curvegenerating method for generating the outline of outline font, a typicalBezier curve generation method is described below.

FIG. 3 is an example of the flowchart showing the reproduction processof Bezier curve reproduced by built-in equipment. FIG. 3 is describedwith reference to FIGS. 4 and 5. Firstly, the control device in built-inequipment reads the data of predetermined starting point, end point andcontrol points (step 201, hereinafter a step is called “S”).

FIG. 4 explains the functional expression of Bezier curve. Bezier curveis used in PostScript font and the like. A used Bezier functionexpresses a cubic approximate curve. If it is assumed that the startingpoint, end point and two control points of the curve are (x₁, y₁), (x₄,y₄), and (x₂, y₂) and (x₃, y₃), respectively, coordinates on Beziercurve, that is, coordinates (x, y) on a character coordinate system isexpressed as follows.X=(1−t)³ x ₁+(1−t)³ tX ₂+3(1−t)t ² x ₃ +t ³ X ₄  (1)y=(1−t)³ y ₁+(1−t)³ ty ₂+3(1−t)t ² y ₃ +t ³ y ₄  (2)0≦n t≦1  (3)

FIG. 5 explains the subdivision method of Bezier curve. As shown byequations (1) through (3), coordinates constituting Bezier curve arecalculated using t as a parameter. In the actual calculation, each ofthe starting point, end point and control points of the curve issubdivided and the coordinates of each control point are calculated.Then, each distance between the control points is calculated, and if thedistance is less than the pixel size of a display, the calculationterminates. If the distance exceeds the pixel size, the distance isfurther subdivided and its coordinate position is calculated.

FIG. 5 is described in detail below. Firstly, a starting point, twocontrol points and end point are assumed to be P1, P2, P3 and P4,respectively. By calculating the middle points these points (S202),middle points P5, P6 and P7 can be obtained between P2 and P3, P3 andP4, and PS and P6, respectively. Furthermore, middle points P8, P9 andP10 can be obtained between P5 and P6, P6 and P7, and P8 and P9,respectively.

P10 is used as its end point on the dividing line 1 side, and as itsstarting point on the dividing line 2 side (S203). Specifically, on thedividing line 1 side, starting point, two control points and end pointare P1, P5, P8 and P10, respectively. On the dividing line 2 side, theyare P10, P9, P8 and P4, respectively.

Then, the distance (length) between the starting and end points iscalculated (S204), and S202 through S204 are repeated until the lengthdrops below the pixel size of a display (S205). In this way, a closedline is sequentially subdivided and the subdivided length is alwaysmonitored. Then, when the length drops below the pixel size, thesubdivision is suspended.

As described above, in outline font, an outline is formed by severalpieces of control point information. Since a personal computer hassufficient processing capacity, time needed to generate a characteroutline can be minimized up to a level sensed by human being.

The reference literatures of the present invention are shown below.

James D. Foley et al., “Computer Graphics Theory and Practice” OhmCorporation.

Haruhiko Okumura et al., “Algorithm Encyclopedia by Java”, TechnicalCriticism Corporation

Satoru Kubota, “Ecology of LCD Display”, Publishing Department, LaborScience Laboratory.

Satoru Kubota, “Character Size, Character Pixel Composition, andRelationship Between Pixel Density and Easiness to Read, of SmallReflective LCD”, Video Information Media Academic Journal, Vol. 55, No.10, pp. 1363-1366 (October 2001).

Kathryn T. Spoehr and Stephen W. Lehmkuhle, “Information Processing ofVisual Angle-Visual-Software of Seeing” translated by Naoyuki Imosake etal., Science Corporation (1986).

However, built-in equipment, such as a cellular phone or the like, hasas much processing capacity as a personal computer. For example, theoperating frequency of a cellular phone is less than 1/10 of that of apersonal computer, and its actual processing capacity is far less that.Therefore, in many cases, the same generation method as a personalcomputer can display no character image within time needed for humaneyes to sense (0.2 seconds), the improvement of whose processing speedis a problem.

Of the outline font generation process, the outline generation processand gradation process take much processing time. The outline generationprocess must perform the distance calculation of divided lines for theentire outline. The gradation process must also perform the calculationfor the entire outline as well as the outline generation process.

SUMMARY OF THE INVENTION

The present invention provides a character image generation program forshortening outline font generation time, a system thereof and a methodthereof. Furthermore, it provides a character image generation programfor shortening its gradating operation processing time, a system thereofand a method thereof.

According to the present invention, a character image generation systemof the present invention, for generating an outline font based oncharacter information including a character code and font informationand displaying it on a display with a predetermined number of pixelscomprises

an acquisition unit for obtaining the character information,

a character outline information storage unit for storing characteroutline information corresponding to the character information,

a subdivision unit for subdividing a curve expressed by the characteroutline information,

a difference calculation unit for calculating the difference betweencoordinates at each end of the subdivided curve,

a comparison unit for comparing the difference with a predeterminedthreshold value, and

an outline coordinate calculation unit for sequentially calculatingcoordinates for each of the pixels, based on the result of thecomparison and specifying it as the coordinate of the outline of eachpixel.

According to the present invention, a storage medium on which isrecorded a character image generation program for enabling a computer toexecute a process of generating outline font, based on characterinformation including a character code and font information anddisplaying the outline font on a display with a prescribed number ofpixels comprising:

an acquiring process for obtaining the character information;

an subdivision process for obtaining the character information from acharacter outline information storage unit for storing character outlineinformation corresponding to the character information and subdividing acurve expressed by the character outline information;

an difference calculation process for calculating a difference betweencoordinates at each end of the subdivided curve;

a comparison process for comparing the difference with a predeterminedthreshold value; and

an outline coordinate calculation process for sequentially calculatingcoordinates for each pixel, based on a result of the comparison andspecifying the coordinates as the coordinates of an outline of eachpixel.

According to the present invention, a character image generation methodfor generating outline font based on character information including acharacter code and font information and displaying the outline font on adisplay with a prescribed number of pixels, comprising:

obtaining the character information;

obtaining the character information from a character outline informationstorage unit for storing character outline information corresponding tothe character information and subdividing a curve expressed by thecharacter outline information;

calculating a difference between coordinates at each end of thesubdivided curve;

comparing the difference with a predetermined threshold value; and

sequentially calculating coordinates for each of the pixels, based on aresult of the comparison and specifying the coordinates as thecoordinates of an outline of each pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows jaggies caused by the change of resolution when usingconventional dot font.

FIG. 2 shows an example of a character expressed by the functionalexpression of conventional Bezier curve.

FIG. 3 is an example of the flowchart showing the reproduction processof Bezier curve reproduced by conventional built-in equipment.

FIG. 4 explains the functional expression of conventional Bezier curve.

FIG. 5 explains the subdivision method of conventional Bezier curve.

FIG. 6 shows the basic configuration of the character image generationsystem of the present invention.

FIG. 7 shows an example of the actual configuration of the characterimage generation system of the present invention.

FIG. 8 is a flowchart showing the character image generation process ofoutline font.

FIG. 9 explains the gradation of an outline.

FIG. 10 is the graph of the resolution of human eyes.

FIGS. 11A and 11B explain approximating a curve to a straight line inthe present invention.

FIG. 12 is the generation flowchart of outline font in the firstpreferred embodiment.

FIG. 13 shows the differences Δx and Δy between a starting point and anend point in the first preferred embodiment.

FIG. 14 shows each enlarged line element of outline font in the firstpreferred embodiment.

FIG. 15 is the generation flowchart of outline font in the secondpreferred embodiment.

FIG. 16 is the generation flowchart of outline font in the thirdpreferred embodiment.

FIG. 17 shows how to obtain the outline coordinates in the thirdpreferred embodiment.

FIG. 18 is the generation flowchart of outline font in the fourthpreferred embodiment.

FIG. 19 shows each enlarged line element of outline font obtained in thefourth preferred embodiment.

FIG. 20 is a flowchart showing the process of generating outline fontand setting gradation in an outline in the fifth preferred embodiment.

FIG. 21 shows how to calculate an area for determining gradation in thefifth preferred embodiment.

FIG. 22 shows a rectangular area in the case where the gradation valueof each line element of outline font obtained in the fifth preferredembodiment is calculated.

FIG. 23 is a flowchart showing the process of generating outline fontand setting gradation in an outline in the sixth preferred embodiment.

FIG. 24 shows how to calculate an area when determining gradation in thesixth preferred embodiment.

FIG. 25 shows an area cut by the outline and each side of a characterimage when calculating the gradation value of each line element ofoutline font obtained in the fifth preferred embodiment.

FIG. 26 is a flowchart showing the process of generating outline fontand setting gradation in an outline in the seventh preferred embodiment.

FIG. 27 shows how to calculate an area for determining gradation in theseventh preferred embodiment.

FIG. 28 is a flowchart showing the process of generating outline fontand setting gradation in an outline in the eighth preferred embodiment.

FIG. 29 shows an example of a correspondence table for determining agradation value in the eighth preferred embodiment (No. 1).

FIG. 30 shows an example of a correspondence table for determining agradation value in the eighth preferred embodiment (No. 2).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 6 shows the basic configuration of the character image generationsystem of the present invention. A character image generation system 100comprises an acquisition unit 101, a subdivision unit 102, a differencecalculation unit 103, a comparison unit 104, an outline coordinatecalculation unit 105, a character outline gradation setting unit 106, acharacter outline information storage unit 107, an inclinationcalculating unit 108 and a correspondence table storage unit 109.

The acquisition unit 101 obtains character information including acharacter code and font information. The character outline informationstorage unit 107 stores character outline information (outline data)corresponding to character information.

The subdivision unit 102 reads character outline informationcorresponding to character information obtained by the acquisition unit101 from the character outline information storage unit 107 andsubdivides a curve expressed by the character outline information. Theinclination calculating unit 108 calculates inclination between eachend, based on the coordinates at each end of the subdivided curve.

The difference calculation unit 103 calculates the difference betweencoordinates at each end of the curve subdivided by the subdivision unit102. The comparison unit 104 compares the difference calculated by thedifference calculation unit 103 and a predetermined threshold value (orlimit value).

The outline coordinate calculation unit 105 sequentially calculatescoordinates for each pixel, based on the comparison result of thecomparison unit 104 and specifies it as the coordinates of the outlineof each pixel. The character outline gradation setting unit 106 sets thegradation of a pixel constituting the character outline, based on thecalculation result of the outline coordinate calculation unit 105.

The correspondence table storage unit 109 stores a table correspondingto a calculated value based an outline obtained by the outlinecoordinate calculation unit 105. Therefore, the character outlinegradation setting unit 106 can also set the gradation of a pixelconstituting the character outline using the corresponding to table.

In this way, outline font can be generated.

According to the present invention, the overhead of a charactergeneration process can be reduced by setting a limit value forsubdividing a curve, using two orthogonal coordinate information in acharacter coordinate system and terminating the subdivision process upto the limit value.

According to the present invention, when calculating an outline, outlinecoordinates can be obtained by incrementing the difference for eachpixel size.

According to the present invention, an outline can also be calculated byobtaining inclination, based on the respective coordinates of a startingpoint and an end point.

According to the present invention, outline coordinates can be obtainedusing the intersection point of the center line of a pixel and anoutline.

According to the present invention outline coordinates can also beobtained using the intersection point of the center line of a pixel andan outline calculated using the inclination against the respectivecoordinates of a starting point and an end point.

According to the present invention, the gradation value of a characteroutline can be obtained based on a character coordinate area cut by anoutline coordinate position.

According to the present invention, the gradation value of a characteroutline can also be obtained based on an area cut by an outline straightline and each side of character coordinates.

According to the present invention, the gradation value of a characteroutline can also be obtained based on the intersection point of anoutline straight line, the center line of a pixel and an outline.

According to the present invention, a gradation value can be calculated,based on the proportional allotment between an outline position and theattribute of coordinates.

According to the present invention, a gradation value can also becalculated, using a correspondence table between an outline position andthe attribute of coordinates.

According to the present invention, a gradation value can be setaccording to an LCD characteristic.

According to the present invention, resolution for realizing printquality can be provided by subdividing a character coordinate systemmore than 64 times a display coordinate system.

FIG. 7 shows an example of the actual configuration of the characterimage generation system of the present invention. A character imagegeneration system 1 comprises at least an input unit 2, a calculationunit 5, a storage unit 9 and a display unit 14.

The input unit 2 obtains text data and font information. For example,the input unit 2 can be a reading device for reading a document datafile 3 for storing text data and font information. Alternatively, theinput unit 2 can be a keyboard 4 for inputting text and font informationby a key operation or the like. The font information is used whengenerating a character image (glyph) from font, and contains at leastthe type of font, font modification data (such as bold, lengthy, etc.)and character size.

The storage unit 9 comprises font memory 10, a limit value settinginformation storage unit 11, a correspondence table storage unit 12,image memory 13 and the like. The font memory 10 stores character font(character generation data). The image memory 13 temporarily stores acharacter image generated by the calculation unit 5 or a character imagecomposed of a plurality of characters.

The storage unit 9 stores limit value setting information. The limitvalue of the difference of each coordinate when subdividing is set asthe limit value. The limit value is at lowest one pixel. Thecorrespondence table storage unit 12 stores a correspondence table forstoring gradation values corresponding to the area ratio of an outlinein one pixel. Furthermore, the storage unit 9 stores the program of thepresent invention. The storage unit 9 also stores a character coordinatesystem obtained by subdividing the display coordinate system of adisplay. In other words, it handles the coordinate system obtained bysubdividing one pixel of the display as character coordinates.

The font memory 10, limit value setting information storage unit 11,correspondence table storage unit 12 and image memory 13 can exist inone storage unit or a plurality of storage units.

The calculation unit 5 at least reads outline data, selects an outlinegeneration method, generates a character outline and generates acharacter image. The calculation unit 5 comprises an outline datareading unit 6, a character outline generation unit 7 and a characterimage generation unit 8. Firstly, the calculation unit 5 converts textdata inputted by the input unit 2 into a character code.

Then, the calculation unit 5 calls up character generation data (outlinedata) corresponding to an inputted text from the font memory 10, basedon a character code and font information. In the case of Bezier curve,the outline data is, for example, a parameter, such as a starting point,an end point and a control point or the like.

Then, in the calculation unit 5 that obtains the outline data, theoutline data reading unit 6 reads the obtained outline data. Then, thecharacter outline generation unit 7 generates a character outline, basedon the read outline data and performs a gradation process. Then, thecharacter image generation unit 8 writes the outline (character outline)generated by the character outline generation unit 7 in the image memory13 and paints out the inside of the outline.

The display unit 14 displays the generated character image.Specifically, the character image written in the image memory 13 isdisplayed on the display unit 14. If the display unit 14 is mounted onportable equipment, in many cases, an LCD panel is used for the reasonthat it must be light.

FIG. 8 is a flowchart showing the character image generation process ofoutline font. In the character image generation system 1, firstly, asdescribed above, the calculation unit 5 obtains curve data from the fontmemory 10, based on font data and UNICODE inputted by the input unit 2.Then, the outline data reading unit 6 reads the outline data (S1).

Then, the character outline generation unit 7 generates an outline,based on the outline data (S2). Thus, a character outline is reproducedin a character coordinate system. In the case of Bezier curve, thecharacter coordinate system is, for example, one expressed by theabove-mentioned equations (1) through (3).

Then, the character outline generation unit 7 applies a gradationprocess to the outline (S3). The gradation process is applied with ananti-aliasing measure. In other words, in order to display a characterhighly precisely, a method for gradating the outline of each pixel asshown in FIGS. 11A and 11B is popular.

Then, the character image generation unit 8 writes the gradated outlinein the image memory 13 (S4). Furthermore, the character image generationunit 8 paints out the inside of a closed curve whose outline isgenerated by the outline (S5).

There is also a method for storing a character center line as data andgenerating a character image by thickening this center line (strokefont).

FIG. 9 explains the gradation of an outline in S3 of FIG. 8. A gradationvalue at the position is determined according to the area from which apixel is cut, based on the location coordinates of the point where thesubdivision is suspended. In FIG. 9, the coordinates (x, y) on theoutline of each pixel are calculated, and a gradation value is set,based on the area ratio of the portion cut by the outline, of eachpixel.

In the present invention, when subdividing an outline, a subdivisionlimit value is set in the difference (Δx, Δy) between a starting pointand an end point. If either a difference in the X axis direction Δx or adifference in the Y axis direction Δy drops below the limited value, thesubdivision process terminates. In this way, process time needed tosubdivide is shortened.

Furthermore, in the present invention, when calculating the outlinecoordinates of the divided curve, the outline coordinates can becalculated by incrementing the coordinates starting from the startingpoint for each pixel size in the direction orthogonal to the axisdirection of a difference that is less than the limit value, based ondifference information between subdivided starting and end points.

In the present invention, a character image is expressed by a charactercoordinate system obtained by dividing at least one pixel by 64×64 inorder to preserve a character design. In the present invention outlinecoordinates are calculated using this character coordinate system. Inthe present invention, after calculating the outline coordinates, thegradation value of the pixel is calculated. The gradation value is setusing the ratio between the outline coordinates and pixel.

Thus, when subdividing a character, the present invention can improvespeed by omitting distance calculation.

The size of a display panel mounted on portable equipment is almostconstant for the reason of a portability requirement. Size easy to read(about 3.5 mm) is used for characters to be displayed on such a displaypanel, and the modification of used size is also restricted to aspecific range around it.

Therefore, if LCD resolution information is known, the number of strokesconstituting a character used in portable equipment is uniquelydetermined. For example, a character of size 3 mm-4 mm is used on adisplay panel of 200 ppi, a character image is composed of 24 through 36dots (pixels).

The longest line element constituting the outline of a character (interms of a Bezier curve, one unit indicated by a curve between startingand end points) is also about 90% of the number of pixels. If a lineelement is subdivided, the length of a line element is furthershortened.

If in the case of a line element composed of several or less pixels, anapproximate curve, such as a Bezier curve is used, the change incurvature of a line element is almost the same as that of a straightline even when control point coordinates are a maximum in the charactercoordinate system. In this case, a curve can be approximately handled asa straight line using a human eye characteristic that change of severaldots or less cannot be recognized on a display panel (see FIG. 10) (seeKathryn T. Spoehr and Stephen W. Lehmkuhle, “Information Processing ofVisual Angle-Software for Seeing” translated by Naoyuki Imosaka et al.,Science Corporation (1986)).

FIG. 10 is the graph of the resolution of human eyes. In FIG. 10,horizontal and vertical axes represent spatial frequency (cycle/degree)and contrast sensitivity, respectively. If image data is considered tobe the distribution of color (density, luminance, etc.), thedistribution can be taken as a wave. For example, the distribution canbe considered to be a pattern (wave) with alternatively repeated lightand darkness, and the repetition can be considered to be a frequency. Inthis case, this frequency is called a “spatial frequency”. If thisspatial frequency is low, the width of a pattern of light and darknessis wide. Conversely, if the spatial frequency is high, the width of apattern of light and darkness is narrow,

As shown in FIG. 10, the contrast reaches a peak when the spatialfrequency is about 5 cycle/degree and decreases after that. Weakcontrast means that light and darkness is difficult to distinguish.Specifically, human eyes become more difficult to perceive in the higherspatial frequency side.

Therefore, as described above, by utilizing a human eye characteristicthat the change of several dots or less cannot be recognized on adisplay panel, a curve can be approximately handled as a straight line.In other words, if the difference in coordinates between the startingand end points of a line element is calculated, the curve of apredetermined difference size between starting and endpoints can beapproximated to a straight line.

Therefore, in the present invention, a curve is approximated to astraight line utilizing the human eye characteristic that the change ofseveral dots or less cannot be recognized on a display panel. This isdescribed below with reference to FIGS. 11A and 11B.

FIGS. 11A and 11B explain approximating a curve to a straight line inthe present invention. FIG. 11A shows, for example, an enlarged Beziercurve on the way of subdivision. As described with reference to FIG. 5,a Bezier curve continues to be subdivided endlessly. However, even if acurve of several dots or less is reproduced on a display panel,attribute to human eye characteristic as described with reference toFIG. 10, the curve cannot be distinguished from a straight lineapproximated to the curve. Therefore, the curve shown in FIG. 11A can beexpressed as a straight line as shown in FIG. 11B. By doing so, theoverhead of curve approximating calculation can be avoided, therebyrealizing the reduction of processing time.

The preferred embodiments of the present invention are described below.Although the present invention is described below using the subdivisionmethod of a Bezier curve as an example, the method is not limited tothis, and another outline generation method is also applicable.

The First Preferred Embodiment

In this preferred embodiment, using the information of XY coordinatesystem, being two orthogonal coordinate systems in a charactercoordinate system, a limit value for subdividing curve is set and asubdivision process is terminated.

FIG. 12 is the generation flowchart of outline font in the firstpreferred embodiment. This flow is executed by the character outlinegeneration unit 7. Firstly, the limit value of the difference betweenstarting and end points for terminating subdivision is set (S11). Thedifference between starting and end points is described with referenceto FIG. 13.

FIG. 13 shows the differences Δx and Δy between starting and end pointsin this preferred embodiment. It is assumed that starting and end pointsare (x₁, y₁) and (x₂, y₂), respectively. In this case, as to the Xcoordinate, a difference Δx=|x₁−x₂| is obtained. As for the Ycoordinate, a difference Δy=|y₁−y₂| is obtained. Hereinafter, Δx and Δyare called the differences between starting and end points. Now, we areback to the description of FIG. 12.

Although in S11, the limit value of the differences Δx and Δy betweenstarting and end points are set, this limit value indicates the numberof pixels needed to accommodate Δx or Δy. For example, the curve shownin FIG. 11A is accommodated by vertical six pixels and horizontal twopixels.

This limit value is determined by the resolution of human eyes andresolution of a display. According to FIG. 10, for example, contrast is10 or less at 80 cycle/degree, and is difficult to be detected by humaneyes. It is assumed that this case is set as a limit value. If theresolution of a display and an observation distance are r ppi (pixel perinch) and L cm, respectively, limit value u is calculated as follows.U=L×tan(1/(80×2))/(25.4/r)For example, if L=0.5 cm and r=1500 ppi, U=3.17. Therefore, if ispassable if 3 or less is set as limit value u.

Then, the data of the starting, end and control points of one lineelement constituting an outline is read from font data (S12). Then, asdescribed with reference to FIG. 5, each of the middle point coordinatesbetween the starting and control points, control points, and control andend points is calculated (S13). Then, as described with reference toFIG. 5, each middle point is modified to starting and end points inorder to subdivide the line element (S14).

Then, the differences Δx and Δy between two orthogonal axes between thestarting and end points of the subdivided line element are calculated(S15). Then, the calculated difference values Δx and Δy are comparedwith the limit value u set in S21 (S16). If as the result of thecomparison in S16, either Δx or Δy drops below the limit value u, (inS16 the process proceeds to “Yes”) the subdivision suspends.

If Δx and Δy are both exceed the limit value u, (in S16 the processproceeds to “No”), each of the middle point coordinates between thestarting and control points, control points, and control and end pointsis further calculated. By modifying each of the coordinates to a middlepoint, the line element is further subdivided (S13 through S15 arerepeated).

If the subdivision suspends, as to an axis direction where thedifferences do not drop below the limit value, in S17 and S18coordinates between the starting and end points are incremented for eachpixel size, and its outline coordinates are calculated. Firstly, as toan axis direction where the differences do not drop below the limitvalue, the coordinates between the modified starting and end modifiedpoints are incremented for each pixel size (S17). For example, in thiscase, it is assumed that the starting and end points are (x₁, y₁) and(x₂, y₂), respectively. If the coordinates in the X axis direction areincremented for each pixel size when Δy drops below the limit value (inthis case, Δx does not drop below the limit value), the coordinatesbecome x₁+1, x₁+2, x₁+3, . . . , x₁+n (n≦x2). In this way, outlinecoordinates continue to be determined in the character coordinate system(S18). S17 and S18 are applied to each subdivided section (between thestarting and end points).

FIG. 14 shows each enlarged line element of outline font in thispreferred embodiment. In FIG. 14, the position of each of the outlinecoordinates at the time of completion of the subdivision is indicated bythe intersection of a cross.

Although in this preferred embodiment, as to an axis direction where thedifferences do not drop below the limit value, the differences areincremented from the starting point toward the end point, as a result,deviation occurs in the position of each end point. For example, ifcoordinates are incremented in the X direction from the starting point,they become (x₁+1, y₁), (x₁+2, y₁), (x₁+3, y₁), . . . , (x₂, y₁). Then,there are two end points (x₂, y₁) and (x₂, y₂), a difference y₂−y₁occurs. In this case, it is OK if the limit value is set in such awaythat y₂−y₁ can be within one pixel.

Thus, by using information about two orthogonal coordinates in thecharacter coordinate system, a limit value for subdividing a curve canbe set and the subdivision process can be terminated at the limit value.Since the number of subdivision processes can be restricted in this way,display speed can be improved, thereby reducing the overhead of acharacter generation process.

Furthermore, since coordinates are incremented and calculated for eachpixel size only one direction, processing speed can also be improved.

The Second Preferred Embodiment

Although in the first preferred embodiment, in either coordinatedirection of the XY coordinate system, the differences between startingand end points are incremented for each pixel size and outlinecoordinates are calculated, in this preferred embodiment, outlinecoordinates are calculated by calculating inclination in coordinatesbetween starting and end points. Parts especially not referred are thesame as in the first preferred embodiment.

FIG. 15 is the generation flowchart of outline font in this preferredembodiment. The character outline generation unit 7 executes this flow.Firstly, the limit value u of the difference between starting and endpoints for terminating subdivision is set to 2 or more (S11 a). S11 a isOK if in S11 of FIG. 12 the limit value u is set to 2 or more.

Then, as in the first preferred embodiment, the data of the starting,end and control points of one line element constituting an outline isread from font data (S12). Then, each of the middle point coordinatesbetween the starting and control points, control points, and control andend points is calculated (S13). Then, each middle point is modified tostarting and end points in order to subdivide the line element (S14).

Then, the differences Δx and Δy between two orthogonal axes between thestarting and end points of the subdivided line element are calculated(S15). Then, the calculated difference values Δx and Δy are comparedwith the limit value u set in S21 (S16). If as the result of thecomparison in S16, either Δx or Δy drops below the limit value u, (inS16 the process proceeds to “Yes”) the subdivision suspends.

If Δx and Δy are both exceed the limit value u, (in S16 the processproceeds to “No”), each of the middle point coordinates between thestarting and control points, control points, and control and end pointsis further calculated. By modifying each of the coordinates to a middlepoint, the line element is further subdivided (S13 through S15 arerepeated).

If the subdivision suspends, as to an axis direction where thedifferences do not drop below the limit value, in S21 through S23,outline coordinates are calculated. Firstly, inclination Δy/Δx betweenstarting and end points is calculated (S21). Then, as to an axisdirection where the differences do not drop below the limit value,coordinates are incremented for each pixel size between modifiedstarting and end points (S22). Then, regarding an outline line as astraight line with the inclination, outline coordinates continue to bedetermined in the character coordinate system (S23).

For example, in this case, it is assumed that the starting and endpoints are (x₁, y₁) and (x₂, y₂), respectively. If the coordinates inthe X axis direction are incremented for each pixel size when Δy dropsbelow the limit value (in this case, Δx does not drop below the limitvalue), the coordinates become x₁+1, x₁+2, x₁+3, . . . , x₁+n (n<x₂). Inthis case, the inclination is obtained, Y coordinate corresponding eachX coordinate is obtained. S21 through S23 is applied to each subdividedsection (between staring and end points).

Thus, two-dimensional coordinates are calculated by calculatinginclination using the respective coordinates of starting and end pointsand incrementing coordinates for each pixel size only in one directionwhen calculating outline coordinates. Since the coordinates of a pointobtained by incrementing for prescribed pixels and the coordinates ofthe essential end point coincide, a large value can be set to the limitvalue.

The Third Preferred Embodiment

In this preferred embodiment, a point obtained by incrementingcoordinates for each pixel size in either of the coordinate systemdirections of the XY coordinate system and plotted is the coordinates ofthe center of each pixel. Parts especially not referred are the same asin the first and second preferred embodiments.

FIG. 16 is the generation flowchart outline font in this preferredembodiment. The character outline generation unit 7 also executes thisflow. As in the first preferred embodiment, the limit value of thedifference between starting and end points for terminating subdivisionis set (S11). Then, as in the first preferred embodiment, the data ofstarting, end and control points of one line element constituting anoutline is read from font data (S12). Each of the middle pointcoordinates between the starting and control points, control points, andcontrol and end points is calculated (S13). Each middle point ismodified to starting and end points in order to subdivide the lineelement (14).

Then, the differences Δx and Δy of two orthogonal axes between thestarting and end points of the subdivided line element are calculated(S15). Then, the calculated differences Δx and Δy are compared with thelimit value set in S11 a. If as a result of the comparison in S15,either Δx or Δy drops below the limit value u, the subdivision suspends.

If Δx and Δy are both exceed the limit value u, (in S16 the processproceeds to “No”), each of the middle point coordinates between thestarting and control points, control points, and control and end pointsis further calculated. By modifying each of the coordinates to a middlepoint, the line element is further subdivided (S13 through S15 arerepeated).

If the subdivision suspends, as to an axis direction where thedifferences do not drop below the limit value, in S31 and S32 outlinecoordinates are calculated. In this preferred embodiment, by calculatingthe coordinates at the center of each pixel between starting and endpoints as to an axis direction where the differences exceeds the limitvalue and calculating coordinates corresponding to the coordinates atthe center as to an axis direction where the differences exceeds thelimit value (S31), outline coordinates are calculated (S32). This isdescribed with reference to FIG. 17. S31 and S32 are applied to eachsubdivided section (between the starting and end points).

FIG. 17 shows how to obtain the outline coordinates in this preferredembodiment. In this preferred embodiment, as to an axis direction wherethe differences do not drop below the limit value, coordinates areincremented for each pixel size between the starting and end points. Inthis case, the center coordinates of each pixel (in this case, centercoordinates in the increment direction) are calculated.

For example, if starting and end points are (x₁, y₁) and (x₂, y₂),respectively, outline coordinates in the X axis direction are obtainedwhen Δy drops below the limit value (in this case, Δx does not dropbelow the limit value). In this case, the center coordinates x_(1h),x_(2h), x_(3h), x_(4h), x_(5h), . . . , x_(nh) (x_(nh)<x₂) in the Xcoordinate of each pixel consecutive from a pixel adjacent to a pixel towhich a starting point belongs are obtained. In this case, it is assumedthat the Y coordinate corresponding to each X coordinate is the Ycoordinate y₁ of the starting point. This process is applied byincrementing coordinates for each pixel size between the starting andend points. In this case, at the Y coordinate of the end point, adifference y₂−y₁ occurs. In this case, it is OK if the limit value isset in such a way that y₂−y₁ can be within one pixel.

Since the number of the subdivision processes can be restricted thus,display speed ca be improved, thereby reducing the overhead of thecharacter generation process.

Furthermore, since coordinates are incremented and calculated for eachpixel size only one direction, processing speed can also be improved.

The Fourth Preferred Embodiment

This preferred embodiment can be obtained by combining the second andthird preferred embodiments.

FIG. 18 is the generation flowchart of outline font in this preferredembodiment. The character outline generation unit 7 also executes thisflow. Firstly, the limit value u of the difference between starting andend points for terminating subdivision is set to 2 or more (S11 a). S11a is OK if in S11 of FIG. 12 the limit value u is set to 2 or more.

Then, as in the first preferred embodiment, the data of the starting,end and control points of one line element constituting an outline isread from font data (S12). Then, each of the middle point coordinatesbetween the starting and control points, control points, and control andend points is calculated (S13). Then, each middle point is modified tostarting and end points in order to subdivide the line element (S14).

Then, the differences Δx and Δy between two orthogonal axes between thestarting and end points of the subdivided line element are calculated(S15). Then, the calculated difference values Δx and Δy are comparedwith the limit value u set in S11 a. If as the result of the comparisonin S15, either Δx or Δy drops below the limit value u, (in S16 theprocess proceeds to “Yes”) the subdivision suspends.

If Δx and Δy are both exceed the limit value u, (in S16 the processproceeds to “No”), each of the middle point coordinates between thestarting and control points, control points, and control and end pointsis further calculated. By modifying each of the coordinates to a middlepoint, the line element is further subdivided (S13 through S15 arerepeated).

If the subdivision suspends, as to an axis direction where thedifferences do not drop below the limit value, outline coordinates arecalculated in S21, S41 and S42. S21 a, S41 and S42 are applied to eachsubdivided section (between the starting and end points) S21 a processincludes S21 and S31. These processes are described in detail below.

Firstly, inclination Δy/Δx between starting and end points is calculated(S21 a (that is, a part of process corresponding to S21)). Then, as inthe third preferred embodiment, the coordinates of the center of eachpixel between the starting and end points is calculated as to an axisdirection where the differences exceed the limit value (S21 a (that is,a part of process corresponding to S31)). As to an axis where thedifferences drop below the limit value, coordinates corresponding to thecenter coordinates are calculated using the inclination Δy/Δx (S41). Inthis way, outline coordinates are calculated (S42).

FIG. 19 shows each enlarged line element of outline font obtained inthis preferred embodiment. FIG. 19 shows the position of the outlinecoordinates at the time of the completion of the subdivision by theintersection of a cross. In each character pixel, the intersectionbetween an outline and a center line is outline coordinates.

Thus, as in the second preferred embodiment, the accuracy of outlinereproduction can be improved and also display speed can be improved,thereby reducing the overhead of the character generation process.

The Fifth Preferred Embodiment

In this preferred embodiment, a gradation value at a character outlineis determined using the outline coordinates calculated in the firstpreferred embodiment.

FIG. 20 is a flowchart showing the process of generating outline fontand setting gradation in an outline in this preferred embodiment. Thecharacter outline generation unit 7 executes this flow. In FIG. 20,outline coordinates are obtained by implementing the first preferredembodiment (S11-S18 in FIG. 12). Then, gradation is calculated accordingto a rectangular area determined by the outline coordinates (S51). Theprocess in S51 is described with reference to FIG. 21.

FIG. 21 shows how to calculate an area for determining gradation in thispreferred embodiment. In FIG. 21, the area distribution of all pixels iscalculated using a ratio up to the intersection position between theoutline and the center line of a pixel and is specified as a gradationvalue.

In FIG. 21A, assuming the center coordinates in the X coordinate of onepixel to be x_(1h), the Y coordinate y₁ on the outline, corresponding tox_(1h) is calculated. Then, the area of a rectangular portion (=lengthof one side of one pixel×y₁) is calculated. In this case, as shown inFIG. 21B, the area ratio of the rectangular portion to one pixel becomes(area of a rectangular area)/(area of one pixel). Therefore, a gradationvalue can be calculated as follows.Gradation value=entire gradation value×(area of a rectangularportion)/(area of one pixel)For example, if area distribution is 0.5 against one pixel, a gradationvalue is 128 against the entire gradation values of 255.

FIG. 22 shows a rectangular area in the case where the gradation valueof each line element of outline font obtained in this preferredembodiment is calculated.

Since by subdividing the character coordinate system into 64 or more ofdisplay coordinate systems, a gradation value is also subdivided inaccordance with it, resolution for realizing high print quality can beobtained.

Thus, a gradation value can be calculated based on an area ration of arectangular portion to each pixel.

The Sixth Preferred Embodiment

In this preferred embodiment, a gradation value in a character outlineis determined using the outline calculated in the second preferredembodiment.

FIG. 23 is a flowchart showing the process of generating outline fontand setting gradation in an outline in this preferred embodiment. Thecharacter outline generation unit 7 executes this flow. In FIG. 23,firstly, outline coordinates are obtained by implementing the secondpreferred embodiment (S11 a-S23 in FIG. 15). Then, an area to be cutaway by an outline and each side of a character image is calculated(S61). Then, a gradation is calculated (S62).

FIG. 24 shows how to calculate an area when determining gradation inthis preferred embodiment. In this preferred embodiment, an areaenclosed by an outline forming a character outline and a side in thecharacter image, of each pixel (slashed portion) is calculated. In thiscase, the area ratio of the slashed portion to one pixel becomes (areaof a slashed portion)/(area of one pixel). Therefore, a gradation valuecan be calculated as follows.Gradation value=entire gradation value×(area of a slashed portion)/(areaof one pixel)For example, if area distribution is 0.5 against one pixel, a gradationvalue is 128 against the entire gradation values of 255.

FIG. 25 shows an area cut by the outline and each side of a characterimage when calculating the gradation value of each line element ofoutline font obtained in this preferred embodiment.

Thus, a gradation value can be calculated based on the area ratio of aslashed portion to each pixel.

The Seventh Preferred Embodiment

In this preferred embodiment, a gradation value in a character outlineis determined using the outline calculated in the third preferredembodiment.

FIG. 26 is a flowchart showing the process of generating outline fontand setting gradation in an outline in this preferred embodiment. Thecharacter outline generation unit 7 executes this flow. In FIG. 26,outline coordinates are obtained by implementing the third preferredembodiment (S11-S32 in FIG. 16). The ratio in height of the locationcoordinates of an intersection to length of a center line is calculated(S71), and a gradation value proportional to the ratio value iscalculated (S72).

FIG. 27 shows how to calculate an area for determining gradation in thispreferred embodiment. In FIG. 27, assuming the length of the center lineof a pixel to be 1, the ratio of the Y coordinate of an intersection tothe length of the center line is calculated and is specified as agradation value.

Firstly, assuming the center coordinates in the X coordinate of onepixel to be x_(1h), Y coordinate y₁ on the outline, corresponding tox_(1h) is calculated. In this case, the ratio of the locationcoordinates of an intersection to a center line is y₁/1.

Therefore, assuming that gradation value=entire gradation value×(y₁/1),a gradation value can be calculated. For example, if the ratio of thelocation coordinates of an intersection to a center line is 0.5 againstpixel size of 1, a gradation value is 128 against the entire gradationvalue of 255.

Thus, a gradation value can be calculated based on the ratio of thelocation coordinates of an intersection to a center line.

The Eighth Preferred Embodiment

FIG. 28 is a flowchart showing the process of generating outline fontand setting gradation in an outline in this preferred embodiment. Thecharacter outline generation unit 7 executes this flow. In FIG. 28,outline coordinates are obtained by implementing the sixth preferredembodiment, and an area cut away by an outline and each side of acharacter image is calculated (S11 a-S61). Then, the ratio of the areacut away by an outline and each side of a character image to the area ofone pixel is calculated. Then, a gradation value is calculated based onthe reference table shown in FIG. 29 or 30 (S81).

The area ratio is calculated as in the sixth preferred embodiment. Inthis case, the area ratio of the slashed portion to the pixel becomes(area of slashed portion)/(area of one pixel).

FIG. 29 shows an example of a correspondence table for determining agradation value in this preferred embodiment (No. 1). FIG. 29 shows anexample of the correspondence table in the case where an area and agradation value are in linear proportion. If the area ratio is 2/2.5, agradation value is 2 according to the table in FIG. 29.

It is OK even if an area and a gradation value are not in linearproportion. Therefore, a gradation value can also be obtained using acharacteristic peculiar to an LCD display device, such as a γcharacteristic value.

FIG. 30 shows an example of a correspondence table for determining agradation value in this preferred embodiment (No. 2). In thiscorrespondence table, a gradation value corresponding to any area ratiois a γ characteristic. For example, if the area ratio is 0.006, agradation value is 5 according to the table in FIG. 30.

As described above, according to this preferred embodiment, an outlinecan be displayed with optimal gradation by selecting a correspondingtable according to a display environment and usage.

The first through eighth preferred embodiments can also be combinedaccording to usage.

Using the present invention, in a display device mounted on built-inequipment, processing speed can be improved while suppressing thequality degradation of a character image.

1. A character image generation system for generating outline font basedon character information including a character code and font informationand displaying the outline font on a display with a prescribed number ofpixels, comprising: an acquisition unit for obtaining the characterinformation; a character outline information storage unit for storingcharacter outline information corresponding to the characterinformation; a subdivision unit for subdividing a curve expressed by thecharacter outline information; a difference calculation unit forcalculating a difference between coordinates at each end of thesubdivided curve; a comparison unit for comparing the difference with athreshold value determined on the basis of a resolution of the display,to approximate a line element of the outline font to a straight line;and an outline coordinate calculation unit for sequentially calculatingcoordinates for each of the pixels, based on a result of the comparisonand specifying the coordinates as the coordinates of an outline of eachpixel, wherein subdivision unit performs the subdivision until a lineelement between the coordinates can be approximated to a straight line,based on the result of the comparison by the comparison unit.
 2. Thecharacter image generation system according to claim 1, wherein thedifference is expressed by two orthogonal axes coordinate systemcomposed of a first factor and a second factor, and when said comparisonunit determines that either value of the first factor or the secondfactor is equal to or less than the threshold value, said subdivisionunit terminates.
 3. The character image generation system according toclaim 2, wherein said outline coordinate calculation unit sequentiallycalculates coordinates for each pixel from one end of the subdividedcurve toward the other end in a direction indicated by a factordifferent from a factor in which said comparison unit determines thatthe difference is equal to or less than the threshold value.
 4. Thecharacter image generation system according to claim 1, furthercomprising an inclination calculation unit for calculating inclinationbetween both the ends, based on the coordinates at each end of thesubdivided curve, wherein said outline coordinate calculation unitsequentially calculates coordinates for each pixel, based on theinclination and specifies the coordinates as coordinates of an outlineof each pixel.
 5. The character image generation system according toclaim 3, wherein the coordinates calculated for each pixel is centercoordinates of each pixel in a direction indicated by a factor differentfrom a factor in which said comparison unit determines that thedifference is equal to or less than the threshold value.
 6. A characterimage generation system for generating outline font based on characterinformation including a character code and font information anddisplaying the outline font on a display with a prescribed number ofpixels, comprising: an acquisition unit for obtaining the characterinformation; a character outline information storage unit for storingcharacter outline information corresponding to the characterinformation; a subdivision unit for subdividing a curve expressed by thecharacter outline information; a difference calculation unit forcalculating a difference between coordinates at each end of thesubdivided curve; a comparison unit for comparing the difference with apredetermined threshold value; an outline coordinate calculation unitfor sequentially calculating coordinates for each of the pixels, basedon a result of the comparison and specifying the coordinates as thecoordinates of an outline of each pixel; and a character outlinegradation setting unit for setting gradation of a pixel forming thecharacter outline, based on the calculation result of said outlinecoordinate calculation unit, wherein the character outline gradationsetting unit calculates the gradation, based on an area ratio between anarea of one pixel forming the character outline and a rectangular areawhose side includes the coordinates calculated by said outlinecoordinate calculation unit or an ratio between an area of one pixelforming the character outline and an area cut way by the outline in apixel forming the character outline.
 7. The character image generationsystem according to claim 6, further comprising a correspondence tablestorage unit for storing a correspondence table in which a gradationvalue corresponding to the ratio between the area of one pixel formingthe character outline and the rectangular area or a correspondence tablein which a gradation value corresponding to the ratio between the areaof one pixel forming the character outline and the area of the cutportion, wherein said character outline gradation setting unit sets thegradation, based on the correspondence table.
 8. A character imagegeneration system for generating outline font based on characterinformation including a character code and font information anddisplaying the outline font on a display with a prescribed number ofpixels, comprising: an acquisition unit for obtaining the characterinformation; a character outline information storage unit for storingcharacter outline information corresponding to the characterinformation; a subdivision unit for subdividing a curve expressed by thecharacter outline information; a difference calculation unit forcalculating a difference between coordinates at each end of thesubdivided curve, wherein the difference is expressed by two orthogonalaxes coordinate system composed of a first factor and a second factor; acomparison unit for comparing the difference with a predeterminedthreshold value, wherein when said comparison unit determines thateither value of the first factor or the second factor is equal to orless than the threshold value, said subdivision unit terminates; anoutline coordinate calculation unit for sequentially calculatingcoordinates for each of the pixels, based on a result of the comparisonand specifying the coordinates as the coordinates of an outline of eachpixel, wherein said outline coordinate calculation unit sequentiallycalculates coordinates for each pixel from one end of the subdividedcurve toward the other end in a direction indicated by a factordifferent from a factor in which said comparison unit determines thatthe difference is equal to or less than the threshold value; and acharacter outline gradation setting unit for setting gradation of apixel forming the character outline, based on the calculation result ofsaid outline coordinate calculation unit, wherein the coordinatescalculated for each pixel is center coordinates of each pixel in adirection indicated by a factor different from a factor in which saidcomparison unit determines that the difference is equal to or less thanthe threshold value, and the length of the center line is equal to thelength of one side of the pixel, and said character outline gradationsetting unit calculates an intersection between a center line of eachpixel forming the character outline expressed by the outline and theoutline and calculates the gradation, based on a ratio between thelength of the center line and a distance between one end of the centerline and the intersection.
 9. The character image generation systemaccording to claim 8, further comprising a correspondence table storageunit for storing a correspondence table in which a gradation valuecorresponding to the ratio between the length of the center line and adistance between one end of the center line and the intersection,wherein said character outline gradation setting unit sets thegradation, based on the correspondence table.
 10. A storage medium onwhich is recorded a character image generation program for enabling acomputer to execute a process of generating outline font, based oncharacter information including a character code and font informationand displaying the outline font on a display with a prescribed number ofpixels comprising: an acquiring process for obtaining the characterinformation; a subdivision process for obtaining the characterinformation from a character outline information storage unit forstoring character outline information corresponding to the characterinformation and subdividing a curve expressed by the character outlineinformation; a difference calculation process for calculating adifference between coordinates at each end of the subdivided curve; acomparison process for comparing the difference with a threshold valuedetermined on the basis of a resolution of the display, to approximate aline element of the outline font to a straight line; and an outlinecoordinate calculation process for sequentially calculating coordinatesfor each pixel, based on a result of the comparison and specifying thecoordinates as the coordinates of an outline of each pixel, wherein thesubdivision process performs the subdivision until a line elementbetween the coordinates can be approximated to a straight line, based onthe result of the comparison by the comparison process.
 11. The storagemedium according to claim 10, wherein the difference is expressed by twoorthogonal axes coordinate system composed of a first factor and asecond factor, and when said comparison process determines that eithervalue of the first factor or the second factor is equal to or less thanthe threshold value, said subdivision process terminates.
 12. Thestorage medium according to claim 11, wherein said outline coordinatecalculation process sequentially calculates coordinates for each pixelfrom one end of the subdivided curve toward the other end in a directionindicated by a factor different from a factor in which in saidcomparison process it is determined that the difference is equal to orless than the threshold value.
 13. The storage medium according to claim10, further comprising an inclination calculation process forcalculating inclination between both the ends, based on the coordinatesat each end of the subdivided curve, wherein said outline coordinatecalculation process sequentially calculates coordinates for each pixel,based on the inclination.
 14. The storage medium according to claim 12,wherein the coordinates calculated for each pixel is center coordinatesof each pixel in a direction indicated by a factor different from afactor in which in said comparison process it is determined that thedifference is equal to or less than the threshold value.
 15. A storagemedium on which is recorded a character image generation program forenabling a computer to execute a process of generating outline font,based on character information including a character code and fontinformation and displaying the outline font on a display with aprescribed number of pixels comprising: an acquiring process forobtaining the character information; a subdivision process for obtainingthe character information from a character outline information storageunit for storing character outline information corresponding to thecharacter information and subdividing a curve expressed by the characteroutline information; a difference calculation process for calculating adifference between coordinates at each end of the subdivided curve; acomparison process for comparing the difference with a predeterminedthreshold value; an outline coordinate calculation process forsequentially calculating coordinates for each pixel, based on a resultof the comparison and specifying the coordinates as the coordinates ofan outline of each pixel; and a character outline gradation settingprocess for setting gradation of a pixel forming the character outline,based on a calculation result of said outline coordinate calculationprocess, wherein the character outline gradation setting processcalculates the gradation, based on an area ratio between an area of onepixel forming the character outline and a rectangular area whose sideincludes the coordinates calculated in said outline coordinatecalculation process or an ratio between an area of one pixel forming thecharacter outline and an area cut way by the outline in a pixel formingthe character outline.
 16. The storage medium according to claim 15,wherein said character outline gradation setting process sets thegradation, based on an area ratio between an area of one pixel formingthe character outline and a rectangular area whose side includes thecoordinates calculated in said outline coordinate calculation process oran ratio between an area of one pixel forming the character outline andan area cut way by the outline in a pixel forming the character outline.17. A storage medium on which is recorded a character image generationprogram for enabling a computer to execute a process of generatingoutline font, based on character information including a character codeand font information and displaying the outline font on a display with aprescribed number of pixels comprising: an acquiring process forobtaining the character information; a subdivision process for obtainingthe character information from a character outline information storageunit for storing character outline information corresponding to thecharacter information and subdividing a curve expressed by the characteroutline information; a difference calculation process for calculating adifference between coordinates at each end of the subdivided curve,wherein the difference is expressed by two orthogonal axes coordinatesystem composed of a first factor and a second factor; a comparisonprocess for comparing the difference with a predetermined thresholdvalue, wherein when said comparison process determines that either valueof the first factor or the second factor is equal to or less than thethreshold value, said subdivision process terminates; and an outlinecoordinate calculation process for sequentially calculating coordinatesfor each pixel, based on a result of the comparison and specifying thecoordinates as the coordinates of an outline of each pixel, wherein saidoutline coordinate calculation process sequentially calculatescoordinates for each pixel from one end of the subdivided curve towardthe other end in a direction indicated by a factor different from afactor in which in said comparison process it is determined that thedifference is equal to or less than the threshold value; and a characteroutline gradation setting process for setting gradation of a pixelforming the character outline, based on a calculation result of saidoutline coordinate calculation process, wherein said character outlinegradation setting process calculates an intersection between a centerline of each pixel forming the character outline expressed by theoutline and the outline and calculates the gradation, based on a ratiobetween the length of the center line and a distance between one end ofthe center line and the intersection, wherein the coordinates calculatedfor each pixel is center coordinates of each pixel in a directionindicated by a factor different from a factor in which in saidcomparison process it is determined that the difference is equal to orless than the threshold value.
 18. The storage medium according to claim17, wherein said character outline gradation setting process sets thegradation, based on a correspondence table in which a gradation valuecorresponding to the ratio between the length of the center line and adistance between one end of the center line and the intersection.
 19. Acharacter image generation method for generating outline font based oncharacter information including a character code and font informationand displaying the outline font on a display with a prescribed number ofpixels, comprising: obtaining the character information; obtaining thecharacter information from a character outline information storage unitfor storing character outline information corresponding to the characterinformation and subdividing a curve expressed by the character outlineinformation; calculating a difference between coordinates at each end ofthe subdivided curve; comparing the difference with a threshold valuedetermined on the basis of a resolution of the display, to approximate aline element of the outline font to a straight line; sequentiallycalculating coordinates for each of the pixels, based on a result of thecomparison and specifying the coordinates as the coordinates of anoutline of each pixel; and displaying the outline font on a display,wherein the subdividing performs the subdivision until a line elementbetween the coordinates can be approximated to a straight line, based onthe result of the comparison.
 20. The character image generation methodaccording to claim 19, wherein the difference is expressed by twoorthogonal axes coordinate system composed of a first factor and asecond factor, and when as a result of the comparison it is determinedthat either value of the first factor or the second factor is equal toor less than the threshold value, the subdivision of the curveterminates.